The origin of trail bikes taken from the 1960s as well as '70s, some trail bikes on show at the Cheshire museum:

In 1975 Ossa Super Pioneer - this 250cc is Hoellerich's preferred racing bike, and there are numerous at his museum. The Ossa bikes were manufactured in Spain, and the company was bust by the early 1980s.
In 1973 Nick Andrews Trail Bike - Six Ossa bikes that were designed by the well-known British trials rider. Andrews signed each one in a recent visit.
In 1963 DOT (Devoid of Trouble) - this unique 250cc bike, bring in from England, was the first with a single front suspension that is coming back in esteem today.

Source: berkshireeagle.com